The invention relates to apparatus and methods for producing bulges in relatively thin metal material, and more particularly, to apparatus and methods for bulging tubes.
There is a great demand for precision metal tubes having enlarged ring-like portions or collars located near one end, especially in the industries in which high pressure fluid connections are needed. Several prior methods of producing precision bulges in metal tubes are known. One method involves use of die elements having a cylindrical hole into which the portion of the tube to be bulged is extended. A ring-like cavity in the hole defines the desired extent of the bulge. An eccentric mandrel is inserted into the open end of the tube, and the outside of the eccentric mandrel is rotated approximately a dozen times or more, causing outward pressure on the inner wall of the tube so that it gradually expands into the cavity and the die, thereby producing the bulge. This type of machine is sometimes referred to as a "beading machine". It has the shortcoming that it causes thinning of the portion of the tubing in which the bulge is formed. Of course, thinning of the wall of the tubing greatly weakens it (since the thinned material in the bulge is known to have a greatly increased tendency to split or fracture), thereby limiting the depth of the bulge that can be formed.
For approximately the past ten years, I have supplied bulged tubes to the industry by utilizing a machine and process, the details of which I have maintained as a trade secret. This machine utilizes die similar to those described above for the beading machines. A mandrel having a channel therein for conducting high pressure oil is inserted into the open end of the tube when the tube is positioned in the die so that the portion in which the bulge is to be formed is aligned with the ring-shaped bulge cavity in the die. The channel has an opening that is generally aligned with the ring-shaped bulge cavity. First and second O-rings disposed in corresponding grooves around the periphery of the mandrel seal the portion of the mandrel between the two O-rings relative to the die. Oil is then pumped at extremely high pressure through the channel, thereby forcing the portion of the tube to be bulged into the ring-shaped bulge cavity. This has been the most successful known approach to producing bulges having the specifications required by the industry. However, this approach also involves thinning of the portion of the tube in which the bulge is formed, and the depth or height of the bulge is therefore also necessarily limited.
There exists a demand for precision bulged tubes having depths greater than those achievable by the above mentioned beading machines or by means of my earlier machine. Therefore, it is an object of the invention to provide an improved tube bulging apparatus and method.
It is another object of the invention to provide an improved tube bulging apparatus and method that avoids excessive thinning of tube material in the region in which a bulge is formed.
It is another object of the invention to provide a tube bulging machine and method capable of producing high precision bulged tubes having bulge depths greater than has previously been achievable.
It is another object of the invention to provide an apparatus and method for forming a relatively large bulge in a relatively thin piece of metal without causing excessive thinning and weakening of the metal material in which the bulge is formed.